What is air recirculation's treatment in 62.1?

• A. Recirculated air is never allowed with outdoor air mixing.
• B. Recirculated air can be used with outdoor air mixed in; it must meet IAQ and filtration requirements.
• C. Recirculated air should always be used to maximize energy efficiency without IAQ considerations.
• D. Recirculation is prohibited in all healthcare facilities.

Answer: (B)

In ASHRAE 62.1, you can use a mix of outdoor air and recirculated indoor air to supply spaces. Recirculation is allowed because it can save energy, but it must not compromise indoor air quality. The air that is recirculated, when blended with outdoor air to meet the minimum outdoor ventilation rate, must pass through filtration and other IAQ controls to meet the standard’s requirements. That’s why the correct approach is that recirculated air can be used with outdoor air mixed in, and it must satisfy IAQ and filtration requirements. The other ideas—recirculation being never allowed with mixing, or being used without IAQ considerations, or being prohibited in healthcare—don’t align with how 62.1 treats ventilation and IAQ control.